Epoxy resins are suitable for a wide range of applications in industry as coatings, adhesives, encapsulants, moldings, laminates, castings, electrical insulation, weatherable coatings, sealants, impregnants, plasticizers, fibers, foams, and the like. Commonly used epoxy resin in such industries is diglycidyl ether of bisphenol. Epoxy resins having glycidyl groups linked to aromatic amino groups, for example, N,N,N′,N′-Tetraglycidyl-4,4′-Diaminodiphenylmethane (TGDDM) are preferred in industries which require good performance at high temperatures such as aerospace industry. Such compounds are usually prepared by reacting an amine which contains at least one aromatic aminohydrogen atom with about 0.8 to 10 equivalents of epichlorohydrin per aminohydrogen atom, followed by conventional dehydrochlorination of the product so obtained using bases. The aromatic N-glycidylamine obtained from the process can be purified and cured by any known methods. The process can be carried out with or without a catalyst. For example, the process disclosed in the U.S. Pat. No. 4,540,769 involves use of an acidic catalyst. However, the disclosed process uses sodium flakes and is exothermic in nature and therefore not suitable for industrial production of the aromatic N-glycidylamine.
Further, the conventionally known processes for preparation of the aromatic N-glycidylamine either provide a highly viscous product or require long reaction time and/or high reaction temperature conditions and/or use solvents for the catalysts that require specific safety measures.
The highly viscous product is obtained due to secondary reactions taking place during the process. Examples of the secondary reactions include coupling reactions. To avoid drawbacks associated with the highly viscous product, inert or reactive diluents are used. However, the use of the inert or reactive diluents can adversely affect the properties of a cured resin. Further, if inert diluents are used then the same are required to be removed completely before curing due to their flammability or toxicity.
Therefore, there is a need of a process for preparation of the aromatic N-glycidylamine, which avoids the drawbacks associated with the conventional processes. Specifically, there is a need for a process that provides highly pure aromatic N-glycidylamine having lower viscosity. At the same time, it is desired that the process is rapid and has high yield. It is also desired that such process involves use of solvent(s) for the catalysts that do not require specific safety measures and produce fewer by-products such as oligomers.